Method for mapping heart electrophysiology

ABSTRACT

A mapping catheter is positioned in a heart chamber, and active electrode sites are activated to impose an electric field within the chamber. The blood volume and wall motion modulates the electric field, which is detected by passive electrode sites on the preferred catheter. Electrophysiology measurements, as well as geometry measurements, are taken from the passive electrodes and used to display a map of intrinsic heart activity.

CROSS REFERENCED TO RELATED CASES

This application is a continuation of Ser. No. 09/005,105, filed Jan. 9,1998, now abandoned, which is a continuation-in-part of Ser. No.08/387,832, filed May 26, 1995, now U.S. Pat. No. 6,240,307, which is anational stage application of PCT/US93/09015, filed Sep. 23, 1993, whichin turn claims priority from U.S. Ser. No. 07/950,448, filed Sep. 23,1992, now U.S. Pat. No. 5,297,549 and U.S. Ser. No. 07/949,690, filedSeptember 23, 1992, now U.S. Pat. No. 5,311,866.

FIELD OF THE INVENTION

The parent invention relates to electrophysiology apparatus which isused to measure and to visualize electrical activity occurring in apatient's heart. The system can display both a visual map of theunderlying electrical activity originating in a chamber of a patient'sheart and the location of a therapy catheter located within a heartchamber. The electrophysiology apparatus includes several subsystemsincluding: a therapy catheter system, a measurement catheter system anda computer based signal acquisition, control and display system.

BACKROUND OF THE INVENTION

Many cardiac tachyarrhythmias are caused by conduction defects whichinterfere with the normal propagation of electrical signals in apatient's heart. These arrhythmias may be treated electrically,pharmacologically or surgically. The optimal therapeutic approach totreat a particular tachyarrhythmia depends upon the nature and locationof the underlying conduction defect. For this reason electrophysiologicmapping is used to explore the electrical activity of the heart during atachyarrhythmic episode. The typical electrophysiologic mappingprocedure involves positioning an electrode system within the heart.Electrical measurements are made which reveal the electrical propagationof activity in the heart. If ablation is the indicated therapy then atherapy catheter is positioned at the desired location within the heartand energy is delivered to the therapy catheter to ablate the tissue.

There are numerous problems associated with these electrophysidlogicdiagnostic and therapeutic procedures. First the testing goes on withina beating heart. The motion of the diagnostic catheter and treatmentcatheter can injure the heart and provoke bouts of arrhythmia whichinterfere with the collection of diagnostic information. During thedelivery of ablation therapy it is common to use fluoroscopic equipmentto visualize the location of the catheters. Many physicians areconcerned about routine occupational exposure to X-rays. In addition,the traditional mapping techniques do not provide a high resolution viewof the electrical activity of the heart which makes it difficult toprecisely locate the source of the arrhythmia.

SUMMARY

The electrophysiology apparatus of the invention is partitioned intoseveral interconnected subsystems. The measurement catheter systemintroduces a modulated electric field into the heart chamber. The bloodvolume and the moving heart wall surface modify the applied electricfield. Electrode sites within the heart chamber passively monitor themodifications to the field and a dynamic representation of the locationof the interior wall of the heart is developed for display to thephysician. Electrophysiologic signals generated by the heart itself arealso measured at electrode sites within the heart and these signals arelow pass filtered and displayed along with the dynamic wallrepresentation. This composite dynamic electrophysiologic map may bedisplayed and used to diagnose the underlying arrhythmia.

A therapy catheter system can also be introduced into the heart chamber.A modulated electrical field delivered to an electrode on this therapycatheter can be used to show the location of the therapy catheter withinthe heart. The therapy catheter location can be displayed on the dynamicelectrophysiologic map in real time along with the other diagnosticinformation. Thus the therapy catheter location can be displayed alongwith the intrinsic or provoked electrical activity of the heart to showthe relative position of the therapy catheter tip to the electricalactivity originating within the heart itself. Consequently the dynamicelectrophysiology map can be used by the physician to guide the therapycatheter to any desired location within the heart.

The dynamic electrophysiologic map is produced in a step-wise process.First, the interior shape of the heart is determined. This informationis derived from a sequence of geometric measurements related to themodulation of the applied electric field. Knowledge of the dynamic shapeof the heart is used to generate a representation of the interiorsurface of the heart.

Next, the intrinsic electrical activity of the heart is measured. Thesignals of physiologic origin are passively detected and processed suchthat the magnitude of the potentials on the wall surface may bedisplayed on the wall surface representation. The measured electricalactivity may be displayed on the wall surface representation in any of avariety of formats. Finally, a location current may be delivered to atherapy catheter within the same chamber. The potential sensed from thiscurrent may be processed to determine the relative or absolute locationof the therapy catheter within the chamber.

These various processes can occur sequentially or simultaneously severalhundred times a second to give a continuous image of heart activity andthe location of the therapy device.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary and illustrative form of the invention is shown in thedrawings and identical reference numerals refer to equivalent structurethroughout.

FIG. 1 is a schematic block diagram of the electrophysiology apparatus;

FIG. 2 is a block diagram representing the partitioning of theelectrophysiology apparatus;

FIG. 3 is a diagram of an illustrative balloon electrode setimplementation of the measurement catheter and a therapy catheter;

FIG. 4 is a schematic diagram of an illustrative basket electrode setimplementation of the measurement catheter;

FIG. 5 is a flow chart showing the wall surface generation process;

FIG. 6 is a schematic diagram of a row of electrodes of the ballooncatheter and their use in measuring distance to the heart chamber wall;

FIG. 7 is a screen display representing the motion of the cardiac wallsurface;

FIG. 8 is a schematic block diagram of the portion of theelectrophysiology apparatus which implements the body orientationgeneration process;

FIG. 9 is a flow charting showing the body orientation generationprocess;

FIG. 10 is a flow chart showing the wall electrogram generation process;

FIG. 11 is a representative screen display showing wall electrograminformation;

FIG. 12 is a representative screen display showing wall electrograminformation;

FIG. 13 is a representative screen display showing wall electrograminformation;

FIG. 14 is a flow chart showing the site electrogram generation process;and

FIG. 15 is a flow chart showing the movable electrode location process.

FIG. 16 is a schematic block diagram of the therapy catheter system;

FIG. 17 is a schematic diagram of the laser delivery embodiment of thetherapy catheter;

FIG. 18 is a schematic diagram of a microwave delivery embodiment of thetherapy catheter;

FIG. 19 is a schematic diagram of a chemical delivery embodiment of thetherapy catheter; and

FIG. 20 is a schematic diagram of the angioplasty catheter embodiment ofthe therapy catheter.

DETAILED DESCRIPTION

FIG. 1 shows the electrophysiologic apparatus 10 connected to a patient12. In a typical procedure a monitoring catheter system 14 is placed inthe heart 16 to generate a display of the electrical activity of theheart 16. After diagnosis a therapy catheter 18 may be inserted into theheart to perform ablation or other corrective treatment.

The monitoring catheter 14 has a proximal end 20 which may bemanipulated by the attending physician, and a distal end 22 whichcarries a monitoring catheter electrode set 44. In general the distalend 22 of the monitoring catheter 14 will be relatively small and willfloat freely in the heart chamber. The therapy catheter 18 has a distalend 24 which carries a therapy catheter electrode set 46. The therapycatheter also has proximal end 26 which can be manipulated by theattending physician.

The electrode sets located on the catheters are coupled to an interfacesystem 28, through appropriate cables. The cable 30 connects themonitoring catheter electrode set 44 to the interface system 28 whilecable 32 connects the therapy catheter electrode set 46 to the interfacesystem 28. The interface system 28 contains a number of subsystems whichare controlled by a computer 34. The data collected by the interfacesystem 28 is manipulated by the computer 34 and displayed on a displaydevice 36. Surface electrodes represented by electrode 40 may also becoupled to the electrophysiology apparatus 10 for several purposes viaan appropriate cable 42. A therapy generator 38 is connected to thetherapy catheter electrode 60 and to the therapy surface ground 70,through the interface system 28. The skin surface electrode cable 42couples the ECG surface electrodes 74 to the ECG system 39, which may bea subsystem of interface system 28.

FIG. 2 is a schematic diagram showing an illustrative segmentation ofthe electrode sets and their electrical connections to subsystems in theelectrophysiology apparatus 10. For example the monitoring electrode set44 contains a subset of passive electrodes 48 which are connected to asignal conditioner 50. The monitoring electrode set 44 also contains asubset of active electrodes 52 which are connected to a signal generator54 through a switch 59. The signal generator 54 is controlled by thecomputer 34. In operation, the signal generator 54 generates a burst of(4800 Hz for example) signals which are supplied to the active electrodeset 52. This energy sets up an electric field within the heart 16chamber. The electrical potentials present on the passive electrode set48 represent the summation of the underlying electrophysiologicalsignals generated by the heart and the field induced by the burst. Thesignal conditioner 50 separates these two components. The preferredtechnique is to separate the signals based upon their frequency.

The high pass section 56 of the signal conditioner extracts the inducedfield signals as modulated by the blood volume and the changing positionof the chamber walls 125. First, the signals are amplified with a gainof approximately 500 from passive electrodes 48 with amplifier 151.Next, the signals are high pass filtered at roughly 1200 Hz by filter153. Then the 4800 Hz signal is extracted by demodulator 155. Finally,the individual signals are converted to digital format by the analog todigital converter 157 before being sent to the computer 34.

The low pass section 58 of the signal conditioner 50 extractsphysiologic signals. First, signal drift is reduced with a 0.01 Hz highpass filter 143. Next, a programmable gain amplifier 145 amplifies thesignals. Then a low pass filter 147 removes extraneous high frequencynoise and the signal from the induced field. Finally, the physiologicsignals are converted to digital format by the analog to digitalconverter 149 before being sent to the computer 34.

The therapy catheter electrode set 46 includes at least one therapydelivery electrode 60, and preferably one or more monitoring electrodes62, and one or more locator electrodes 68. The therapy deliveryelectrode 60 cooperates with the ground electrode 70, which is generallya skin patch electrode, to deliver ablation energy to the heart. Theseelectrodes are coupled to the ablation energy generator 38 which isshown as an RF current source. A locator electrode 68 is provided whichis preferably proximate the delivery electrode 60, but can be a separateelectrode site located near the distal end 24 of the therapy catheter18. This electrode site is coupled with an active electrode 52 through aswitch 59 to the signal generator 54. In use, the electric field coupledto the therapy catheter 18 permits the physician to track and visualizethe location of the locator electrode 68 on the display device 36. Thetherapy catheter electrode set 46 can also be used to monitor thephysiologic signals generated at the chamber wall 125 by a low passsignal conditioner 141 which is similar to the low pass section 58 ofthe signal conditioner 50. These digitized signals are then sent to thecomputer 34.

At least one electrode pair 119 of surface electrodes 40 are alsocoupled to the signal generator 54 through switch 59. Each electrode 89and 115 are placed opposite each other on the body surface with theheart 16 in-between them. The induced field is sensed by passiveelectrodes 48 and conditioned by the high pass section 56 of the signalconditioner 50. This field helps the computer 34 align or orient thepassive electrodes 48 to the body for better visualization of the hearton the monitor 36.

The ECG subsystem 39 accepts signals from standard ECG skin electrodes74. It also contains a low pass section similar to the low pass section58 of signal conditioner 50. In general, the passive electrode set 48and active electrode set 52 will reside on a single catheter, however itshould be recognized that other locations and geometries are suitable aswell. Both basket and balloon devices are particularly well suited tothis application.

FIG. 3 shows an electrode configuration on a balloon catheter 94 whichhas an inflatable balloon 96 which underlies an array or set of passiveelectrodes 48 typified by passive electrode 72. These passive electrodes48 can be organized into rows, typified by row 123, and columns,typified by column 121. A pair of active excitation electrodes 52 aretypified by proximal electrode 92 and distal electrode 98. The ballooncatheter 94 configuration can be quite small in comparison with thebasket catheter 80 configuration. This small size is desirable both forinsertion into and for use in a beating heart 16.

FIG. 3 also shows a movable, reference or therapy catheter system 18.This catheter is shown lying along the interior surface 125 of the heart16. A pair of electrodes shown as delivery electrode 60 and referenceelectrode 62 are located a fixed distance apart on the catheter body 64.This auxiliary catheter may be used to supply ablation energy to thetissue during therapy. This therapy catheter 18 may be used with eitherthe basket catheter 60 configuration or the balloon catheter 94configuration.

FIG. 4 shows an electrode configuration on a basket catheter 80. Thelimbs of the basket 80, typified by limb 82 carry multiple passiveelectrode sites typified by electrode 84. A pair of active excitationelectrodes are shown on the central shaft 86 of the basket 80 asindicated by excitation electrode 88. The basket catheter 80 electrodeslie gently against the interior surface 125 of the heart 16 urged intoposition by the resilience of the limbs. The basket catheter 80 permitsunimpeded flow of blood through the heart during the mapping procedurewhich is very desirable. This form of catheter also places theelectrodes into contact with the heart chamber wall 125 for in-contactmapping of the physiologic potentials of the heart 16.

Returning to FIG. 1 and FIG. 2 these figures show one illustrativepartitioning of system functions. In use, the signal generator 54 cangenerate a 4800 Hz sinusoidal signal burst on the active electrode set52 which creates an electric field in the heart. The changing positionof the chamber walls 125 and the amount of blood within the heartdetermines the signal strength present at the passive electrode sites48. For purposes of this disclosure the chamber geometry is derived fromthe electric field as measured at the passive electrode sites 48 whichmay, or may not be in contact with the walls 125 of the heart. In thecase of the basket electrodes 84 which lie on the heart surface 125 thefield strength is inversely proportional to the instantaneous physicalwall location and the distance from the active electrodes 52 to thesewalls. In the case of the balloon catheter the potentials on the passiveset of electrodes 72 are related to the wall location, but a set ofcomputationally intensive field equations must be solved to ascertainthe position of the wall. In general, both the basket and balloonapproach can be used to generate the dynamic representation of the wallsurface.

The computer 34 operates under the control of a stored program whichimplements several control functions and further displays data on adisplay device 36. The principal software processes are the wall surfacegeneration process (WSGP); the body orientation generation process(BOGP); the wall electrogram generation process (WEGP); the siteelectrogram generation process (SEGP); and the movable electrodelocation process (MELP).

WALL SURFACE GENERATION PROCESS

FIG. 5 is a flow chart describing the method used to generate the “wallsurface” of the interior of the heart 16. The step-wise processes arepresented with certain physical parameters which are either known inadvance by computation or are measured. This knowledge or information isshown in block 53, block 55 and block 57. The WSGP process begins atblock 41 with the insertion of the monitoring catheter 14 in the heart16. This catheter 14 places an array of electrodes 44 in a heart 16chamber. This array must have both passive measurement electrode sites48 and active interrogation electrode sites 52 located in a knownposition. The process enters a measurement and display loop at block 43where an interrogation pulse burst is generated by the signal generator54 seen in FIG. 2. These pulses are generated first with the currentsource at site 92 and the current sink at site 98 and second with thecurrent source at site 98 and the sink at site 92 as seen in FIG. 3. Atblock 45 the signal conditioner 50 uses information on the frequency andtiming of the interrogation current from block 53 to demodulate thesignals and analog to digital convert the signals received at thepassive measurement electrodes 48. At block 47 the information fromblock 55 in used. This information includes both the current strength ofthe interrogation pulse and the location of the interrogation source andsink electrodes. Impedance is voltage divided by current. The voltageoffset caused by the location of the current source can be reduced bythe two measurements of opposite polarity. This information is used todetermine the impedance which the chamber and the blood contained inthat chamber imposes on the field generated by the interrogationcurrent. The knowledge from block 57 is used next. Block 49 determineshow the heart chamber tissue, which has roughly three times theimpedance of blood, in combination with the type of electrode arrayaffects the field generated by the interrogation electrodes.

In a system as shown as the basket in FIG. 4 the blood effects theimpedance directly as the field is propagated from the interrogationelectrodes to the measurement electrodes. In general, if a point currentcourse is used within a chamber the inverse of the measured voltage isproportional to the square root of the distance from the source. Withthe distance from each electrode 84 to both excitation electrodes 88computed from the measured voltage and the known location of theelectrodes 84 relative to each other, the locations of each electrode 84can be determined.

In a system as shown in FIG. 3 the impedance of the field generatedwithin the blood volume is modulated by the position of the walls 125,with their higher impedance, with respect to the location relative tothe measurement electrodes. Using this knowledge and the measurementsfrom block 47 the distance from the interrogation electrodes to theheart chamber wall 125 is determined at a point normal to the fieldgenerated by the active interrogation electrodes 52.

The passive electrodes 48 on the balloon catheter 94 can be positionedin rows 123 and columns 121 with the columns in a line from the top ofthe balloon 96 near active electrode 92 to the bottom of the balloon 96near active electrode 98. In a preferred embodiment three configurationsare possible: 8 rows and 8 columns, 7 rows and 9 columns, and 6 rows and10 columns. In each such embodiment the measurements from any row 123are treated independently. Using the 8 row, 8 column embodiment as anexample, 8 measurements of distance are taken for any selected row ofelectrodes, giving a total of 64 measurements.

FIG. 6 is a schematic drawing of the embodiment required to measure thedistance 129 from the centroid 127 of the balloon 96 through the passiveelectrode 131 to the heart chamber wall 125. The passive electrode 131is one of eight electrodes on a row of electrodes 123. Starting withelectrode 131 and labeling it as electrode A, the other electrodes onthe row 123 are labeled B, C, D, E, F, G and H by proceeding around theballoon 96 in a clockwise direction. The measurements of impedance “I”at these electrodes are thus labeled I_(A), I_(B), I_(C), I_(D), I_(E),I_(F), I_(G) and I_(H). To compute the distance 129 in the direction ofelectrode 131 the following equation is computed:ln(D _(A))=c 0+c 1*ln(I _(A))+c 2*ln(I _(B))+c 3*ln(I _(C))+c 4*ln(I_(D))+c 5*ln(I _(E))+c 4*ln(I _(F))+c 3*ln(I _(G))+c 2*ln(I_(H))where D_(A) is the desired distance 129 and c0 through c5 are optimizedparameters. A typical vector of these parameters is (c0, cl, c2, c3, c4,c5)=(3.26, −0.152, −0.124, −0.087, −0.078, −0.066).

Once the distance 129 in the direction of electrode 131 is determinedthen the computation can be redone by shifting this direction clockwiseone electrode, relabeling electrodes A through H and solving the aboveequation again. Once the distances for this row of electrodes 123 aredetermined then the next row distances are determined in the same wayuntil the distances at all 64 electrodes are determined.

Returning to FIG. 5, with multiple wall locations in space determined bythis method, a model of the chamber wall 125 shape can be created inblock 51. Various techniques for creating a shape are possible,including cubic spline fits, and best fit of an ellipsoid. The positionsof the active electrodes 52 and the passive electrodes 48 relative tothe heart 16 chamber walls are also determined at this point. The loopcontinues as the method moves back to block 43. This loop continues at arate fast enough to visualize the real-time wall motion of the heartchamber, at least at twenty times per second.

There are numerous display formats or images which can be used topresent the dynamic endocardial wall surface to the physician. Itappears that one of the most useful is to unfold the endocardial surfaceand project it onto a plane. Wire grid shapes representing a perspectiveview of the interior of the heart chamber are useful as well. It appearsthat each individual physician will develop preferences with respect topreferred output image formats. In general, different views of theendocardial surface will be available or may be used for diagnosis ofarrythmia and the delivery of therapy. One distinct advantage of thepresent invention is that the image of the heart wall is not static orartificial. In this system the image is a measured property of the heartwall, and is displayed in motion.

FIG. 7 shows two separate frames of the dynamic representation of theheart wall. Wire frame 71 shows the heart at systole while wire frame 73shows the heart at diastole. Path arrow 75 and path arrow 77 representthe dynamic cycling through several intermediate shapes between thesystole and diastole representation. These views are useful as theyindicate the mechanical pumping motion of the heart to the physician.

BODY ORIENTATION GENERATION PROCESS

FIG. 8 is a schematic drawing of the apparatus required to perform thebody orientation generation process. It shows a patient 12 with at leastone pair 119 of skin electrodes 40 attached to the body surface in astationary position on the body and in a known configuration. Theseelectrodes are typified by example surface electrodes 89 and 115 each ofwhich could be an ECG electrode 74, an RF generation current sinkelectrode 70, or another electrode specifically dedicated to the BOGP.Ideally, electrode 89 and 115 are opposite one another on the body withthe heart 16 directly in between them. This pair of electrodes isattached to the signal generator 54 through the switch 59 via anappropriate cable 117. The distal end 22 of monitoring catheter 14 issituated in the heart 16 where the passive electrodes 48 can measure thesignals generated across the electrode 89 and electrode 115.

FIG. 9 is a flow chart describing the method used to align the wallsurface representation of the WSGP to the body orientation. The processbegins at step 101 where the monitoring catheter 14 with a set ofpassive electrodes 48 is inserted into heart 16 chamber and a pair ofsurface electrodes 119 are attached at a known position on the body 12.The process begins cycling at step 102 where the signal generator 54generates a signal across the skin electrode 89 and skin electrode 115.At step 103 the voltage created by the signal generator 54 is measuredfrom passive electrode 48 by the high pass section 56 of the signalconditioner 50 by using the information from block 110 which includesthe frequency and timing of the field generated by the signal generator54. This voltage information is stored in an array “Y”.

At step 104 a regression analysis is performed which creates a vectorwhich lines up with the field generated in step 103. This regressionmethod is the same whether a basket catheter as shown in FIG. 4 or aballoon catheter as shown in FIG. 3 is used. The location of eachpassive electrode 48 is provided to the method by block 110. Thisinformation comes from different sources in each case however. In thecase of a basket catheter 80 these three dimensional electrode locationscome from the WSGP. In the case of the balloon catheter 94 these threedimensional electrode locations are known a priori. In each case theyare saved in an array “X”. The regression to compute the orientationvector uses the standard regression equation for the computation of aslope:b=Σxy/Σx ²where “X” is the array of electrode locations, “Y” is the array ofmeasured voltages and “b” is the orientation vector. If more than onepair of skin electrodes are used then an orthogonal set of orientationvectors can be created and any rotation of the monitoring catheter 14relative to the body 12 can be detected.

In step 105 the information on the location of the chamber walls 125from the WSGP 109 can be used to create a three dimensional model of theheart 16 chamber as seen in FIG. 7. By combining this model with thecomputed orientation from step 104 and the known location of the skinelectrodes 108 this representation can be shown in a known orientationrelative to the body in step 106. In step 107 a specific orientationsuch as typical radiological orientations RAO (right anterior oblique),LAO (left anterior oblique), or AP (anterior/posterior) can bepresented. By repeatedly showing this view a dynamic representation canbe presented which matches the view shown on a standard fluoroscopicdisplay. Thus such an image can be presented without the need for usingionizing radiation.

WALL ELECTROGRAM GENERATION PROCESS

FIG. 10 is a flow chart describing the wall electrogram generationprocess (WEGP). This process begins at block 61 when a monitoringcatheter 14 with an array of passive measurement electrodes 48 is placedin a heart chamber 16 and deployed. The process enters a loop at block63. The frequency of the interrogation pulses generated by the signalgenerator 54 is provided by block 85. With this knowledge the low passfilter section 58 of the signal conditioner 50 measures the voltage atfrequencies lower than the generated interrogation pulses. Typically thehighest frequency of the biopotentials is 100 Hz but can be as high as250 Hz.

In the case of a basket system as seen in FIG. 4 the measurements arecontact voltages from the chamber wall 125 tissue contacting theelectrodes 84.

In the case of a balloon system as seen in FIG. 3 the measurements aremeasurements of the field generated throughout the blood volume by thetissue on the chamber wall 125. At step 65, a model of the arrayboundary and the chamber wall 125 boundary is created from theinformation in block 87. This information includes the location of thepassive electrodes 48 on the array and the chamber wall 125 locationsfrom the WSGP.

In the case of a basket system as seen in FIG. 4, the array boundary andthe chamber wall 125 boundary are the same since they are in contact.The locations are determined in three-dimensional space of the sites onthe chamber wall where potentials are measured.

In the case of the balloon system as seen in FIG. 3, the array boundaryand the chamber wall 125 boundary are different. During step 65,locations are generated in three-dimensional space of the sites on thechamber wall where potentials are to be determined.

At step 66, the potentials are projected on to the sites on the chamberwall specified in step 65. In the case of a basket system as seen inFIG. 4, the measured potentials are assigned to these sites.

In case of a balloon system as seen in FIG. 3, a three dimensionaltechnique such as those typically used in field theory is used togenerate a representation of the three dimensional field gradients inthe blood volume of the heart chamber. Two examples of appropriatetechniques are a spherical harmonics solution to Laplace's equation, andboundary element analysis. A more detailed description of sphericalharmonics is given in the parent disclosure which is incorporated byreference herein.

For the boundary element method in the mapping system of the invention,the voltage is measured at the passive electrodes 48 on the probe orballoon catheter 94. From the voltage at the electrodes on the probe andthe knowledge that the probe is nonconducting, the voltage and normalcurrent at a previously selected set of nodes on the endocardial surface125 are determined by the boundary element method in the followingmanner.

It is known that the voltage in the blood pool between the probe and theendocardium satisfies Laplace's equation that states that the netcurrent flow across any specific boundary is zero. To find the voltageand/or normal current on the endocardium, one must find the solution ofLaplace's equation in the blood pool and calculate the values of thissolution on the endocardium. Standard finite element and finitedifference methods can be used to find the solution to Laplace'sequation, but they have large computational overhead for generating andkeeping track of a three-dimensional grid in the whole blood pool. Inthe mapping system of the invention, Laplace's equation is solved by theboundary element method, a specialized finite element method thatpermits one to restrict the calculations to the two-dimensional probeand endocardial surfaces (and not have to deal with calculations overthe blood pool between these two surfaces). In order to create anaccurate map of the endocardial voltage and/or normal current based onthe voltage information from a limited number of electrodes on theprobe, the system uses a higher-order version of the boundary elementmethod. This system currently uses bicubic splines to represent theprobe and endocardial surfaces and bilinear elements and bicubic splinesto represent the voltage and the normal current on these surfaces.

The boundary element method consists of creating and solving a set oflinear equations for the voltage and the normal current on theendocardium based on the voltage measurements at the electrodes on theprobe. Each of the elements in the matrices that are involved in thisset consists of two-dimensional integrals, which are calculated bynumerical and analytical integration.

Using Laplace's equation with data given on the probe is a so-called“ill-posed” problem. For such problems, all solution procedures,including the boundary element method, are ill conditioned, that is,small errors in the measured voltage on the probe surface can result inlarge errors in the calculated voltage and/or normal current on theendocardium. To minimize the errors on the endocardium, options forregularization or constraints have been included in the software code.For example: the user can choose parameters that cause the code to addequations for known or expected values of the voltage and/or normalcurrent on the endocardium. This capability is often but not exclusivelyused to add equations that take into account the voltage and/or normalcurrent of the map of the previous instant(s) in time (the previous“frame(s)”). This process uses historical data from the previous frameto constrain the values subsequently computed.

The solution of the set of the boundary element equations andregularizing equations (if any) is normally accomplished by singularvalue decomposition but there is an option to solve the linear system bydecomposition (Gaussian elimination) or direct or inherent methods. Whensingular value decomposition is used, there is an option to turn off theinfluence of high-frequency errors (that is, do a type ofregularization) by setting various small singular values to zero, theresult of which can be an increase in the accuracy of the calculatedvoltage and normal current on the endocardium.

In block 67, a large number of points are calculated on thethree-dimensional chamber surface 125. In the case of a basket catheteras seen in FIG. 4, this is done through interpolation using bilinear orbicubic splines. In the case of a balloon catheter as seen in FIG. 3,this can be done either by using the model, such as the boundary elementmethod or spherical harmonics to generate more points. Alternatively,bilinear or bicubic splines can be used to interpolate between a smallernumber of points.

In block 69 a representation of the electrical potentials on the surface125 are used to display the patterns. These types of displays includecolor maps, maps of iso-potential lines, maps of potential gradientlines and others. The electro-physiologic information is reconstructedon the dynamic wall surface 125. In general the measured electricalactivity is positioned by the WSGP at the exact location which givesrise to the activity. The high resolution of the system creates anenormous amount of information to display. Several techniques may beused to display this information to the physician. For example theelectrogram data can be shown in false color gray-scale on a twodimensional wall surface representation. In this instance areas of equalpotential areas are shown in the same color. Also a vectorized displayof data can be shown on a wire grid as shown in FIG. 11 where thedistance between any two dots typified by dot pair 91 and 93 represent afixed potential difference. The more active electrical areas showclusters of dots. In a dynamic display the dot movement highlights areasof greater electrical activity. In FIG. 12 gradient lines typified byline 135 represent the change in potential over the chamber wallsurface. Those areas with the largest change per unit area have thelongest gradient lines oriented in the direction of steepest change. InFIG. 13 iso-potential lines typified by line 95 represent equalelectrical potential. In this representation the closeness of linesrepresents more active electrical areas.

SITE ELECTROGRAM GENERATION PROCESS

FIG. 14 is a flow chart of the site electrogram generation process(SEGP). This process is used to extract and display a time seriesrepresentation of the electrical activity at a physician selected site.FIG. 13 shows a site 97 that has been selected and a time serieselectrogram 99 is shown on the display device 36 along with the dynamicwall representation. Returning to FIG. 14 this process begins at block76 when a catheter with an array with both passive measurementelectrodes 48 and active electrodes 52 is placed in a heart chamber anddeployed. The process enters a loop at 78. The inputs to the methodinclude the wall locations from block 37. Then the wall electrogramgenerator 35 provides the electrical potentials on this surface at 79.The user will use the display 36 to determine a location of interest inblock 33 which will then be marked on the display device 36 at step 81.The voltage from this location will be collected at block 83. Thisvoltage will be plotted in a wave-form representation 99 in block 31.The loop continues at this point at a rate sufficient to display all ofthe frequencies of such a time series electrogram 99, at least 300points per second.

The false color and vectorized display images may direct the physicianto specific sites on the endocardial surface for further exploration.The system may allow the physician to “zoom” in on an area to show theelectrical activity in greater detail. Also the physician may select asite on the endocardial wall 125 and display a traditional time serieselectrogram 99 originating at that site.

MOVABLE ELECTRODE LOCATION PROCESS

FIG. 15 is a flow-chart of the movable electrode location process(MELP). It begins at block 11 when a catheter with an array of passivemeasurement electrodes 48 and active electrodes 52 is placed in a heart16 chamber and deployed. At block 13 a second catheter 18 with at leastone electrode is introduced into the same chamber. The process enters aloop at block 15 where the signal generator 54 generates a carriercurrent between the movable location electrode 68 and an activeelectrode 52. At block 17 the high pass section 56 of signal conditioner50, using the frequency and timing information of the location signalfrom block 29, produces measured voltages from the passive measurementelectrodes 48. At block 19 the information from block 27 is used todetermine the location of the electrode 68 where the location current isgenerated. This information includes the strength of the generatedlocation current, the impedances of blood and tissue, the location ofthe active electrode 52 in use and the location of all the passivemeasurement electrodes 48. One method for using this information wouldentail performing a three dimensional triangulation of the point sourcelocation signal using four orthogonal passive electrode 48 sites. Theimplementation of step 19 is the same both for the case of a basketsystem as seen in FIG. 3 and for the case of a balloon system as seen inFIG. 4. In this preferred implementation, two data sets are acquiredclosely spaced in time such that they are effectively instantaneousrelative to the speed of cardiac mechanical activity. Alternatively, thedata sets could be acquired simultaneously, by driving signals at twodifferent frequencies, and separating them electronically by well knownfiltering means.

The first data set is acquired by driving the current carrier from thelocation electrode 68 to a first sink or active electrode as typified byelectrode 98. This electrode is at a known location on the body of themonitoring catheter 14 relative to the array of passive electrodes 48.The location of this first sink electrode is ideally displaced distallyfrom the centroid 127 of the array of electrodes by at least 25millimeters. A second data set is then acquired by driving the currentfrom the location electrode 68 to a second active electrode 92, locatedideally at least 25 millimeters proximally from the centroid 127 of thearray of electrodes.

The location algorithm is performed by minimizing the followingequation:${\sum\limits_{i = 1}^{n}( {\frac{k}{( {{\overset{arrow}{R}}_{i} - {\overset{arrow}{R}}_{1}} )^{0.5}} - V_{{pi}_{1}} - b_{1} - \frac{k}{( {{\overset{arrow}{R}}_{i} - {\overset{arrow}{R}}_{S_{1}}} )^{0.5}}} )^{2}} + ( {\frac{k}{( {{\overset{arrow}{R}}_{i} - {\overset{arrow}{R}}_{1}} )^{0.5}} - V_{{pi}_{2}} - b_{2} - \frac{k}{( {{\overset{arrow}{R}}_{i} - {\overset{arrow}{R}}_{S_{2}}} )^{0.5}}} )^{2}$Where n is the number of array electrodes, where k, b₁ and b₂ arefitting parameters, V_(pi) are the potentials measured from each i^(th)electrode 72, R_(i) is a vector from the origin (centroid of the arrayof electrodes 96) to the i^(th) probe electrode 72, R_(L) is the“location vector”, or three dimensional location to be solved for in theminimization, and R_(s1), R_(s2) are the location vectors of the activesink electrodes (eg. 92 and 98) which are known at locations on the axisof the array of passive electrodes 48.

Additional data sets could be incorporated, following the same logic asabove. Each additional squared parenthetical term requires the probedata set Vpi, another ‘b’ fitting term, and the particular active sinkelectrode 52 vector R_(s) used during the acquisition of that data set.If the sink electrode 52 is far enough away, for example using a rightleg patch electrode, the fourth term in the squared expression for thatdata set may be deleted as R_(s) becomes very large.

It is also noted that the method does not require two data sets. Thefirst squared expression in the above expression (requiring only dataset V_(pi1)) may be sufficiently accurate.

The non-linear least squares minimization may be performed on the abovesummation by any of several well-known methods. The Levenberg-Marquardtmethod has been used in practice to accomplish this with efficient androbust results. Nominal values for k and b are 70 and 0 respectively,when normalizing the potential values obtained as if the current sourcewere 1 ampere. The number of parameters in the minimization for theabove expression are six: k, b₁, b₂, and the x, y, and z coordinates ofvector R_(L) cassuming a Cartesian coordinate system with origin at thecenter of the array of electrodes 96).

At step 21 a model of the heart 16 chamber wall is generated from theinformation provided from the WSGP 25. Such a model can be representedon a display 36 in a manner typified in FIG. 6. Once this surface isrendered, within this surface a second figure representing the distalend of the monitoring catheter 14 can be presented. In this way, thefull three dimensional geometry of the chamber and the array cathetercan be presented.

In step 23 this geometry is updated repeatedly to provide a dynamic viewof the chamber, the monitoring catheter 18, along with a representationof the distal end 24 of the therapy catheter 18. If this is thencombined with the electrical potentials generated by the WEGP, thetherapy catheter can be moved to an electrical site of interestrepresented by a point in three dimensional space.

CALIBRATION PROCESS

Calibration of the system to insure that physical dimensions areaccurately scaled is not a necessity for use of the system in adiagnostic or therapeutic setting. However, the availability of heartgeometry in real time can permit various hemodynamic measurements to bemade and displayed to the physician as well. These measurements includesystolic time intervals, stroke volume and cardiac output. Calibration,where desired, requires at least two electrodes 60 and 62 a knowndistance apart placed along the inner-surface of the heart chamber 16,as shown in FIG. 3. In general the two electrode sites will each becoupled to the location signal generator 54. The MELP of FIG. 15 can becalibrated by scaling the calculations 50 the distance between computedlocations match the known distance apart of the two electrodes 60 and62. Since the electrodes 60 and 62 are positioned on the chamber wall125, the WSGP of FIG. 5 can be calibrated by scaling the distancemeasured by the WSGP in the direction of electrodes 60 and 62 to thecalibrated distances measured by MELP. Finally, since the electrodes arecontacting the chamber wall and providing electrograms, the WEGP of FIG.10 and SEGP of FIG. 14 can be calibrated to those measurements bycomputing the voltages at the same locations on the chamber wall 125where electrodes 60 and 62 are located. These computed voltages can thenbe scaled to match the physically measured voltages from electrodes 60and 62.

THERAPY CATHETER

FIG. 16 is a schematic diagram of the therapy catheter system. Thetherapy catheter 18 has both a distal end 24 and a proximal end 26. Ahandle 163 is on the proximal end 26 which allows the user to manipulatethe distal end 24 and position it in the heart 16. Referring to FIG. 1,this handle also permits the therapy catheter 18 to connect to theinterface system 28 of the electrophysiologic apparatus 10 through thecable 32. The location current is generated by the signal generator 54through the switch 59 and subsequently through the wire 177 of cable 32which is connected directly to the locator electrode 68. The therapycatheter system also includes a therapy generator 38 which is connectedto the therapy catheter handle 163 via therapy supply line 161. Thetherapy supply line 161 extends through the handle 163, through thecatheter body 64, to the therapy deployment apparatus 60 at the distalend 24 of the catheter. The locator electrode 68 is in close proximityto the therapy deployment apparatus 60 in order to determine itslocation within the heart 16.

FIG. 17 shows an embodiment of the therapy catheter 18 using laserenergy to supply the therapy. This laser catheter 165 includes thelocation wire 177 which connects the interface system 28 to the locatorelectrode 68 at the catheter's distal end 24. In this instance thetherapy supply line 161 is a fiber optic cable 167 and the therapydeployment apparatus 60 is a fiber optic terminator 169 which directsthe laser energy to the site of therapy delivery.

FIG. 18 shows an embodiment of the therapy catheter 18 using microwaveenergy to supply the therapy. This microwave catheter 171 includes thelocation wire 177 which connects the interface system 28 to the locatorelectrode 68 at the catheter's distal end 24. In this instance thetherapy supply line 161 is a microwave wave guide 173 and the therapydeployment apparatus 60 is a microwave emitter 175 which directs themicrowave energy to the site of therapy delivery.

FIG. 19 shows an embodiment of the therapy catheter 18 using a chemicalto supply the therapy. This chemical deliver catheter 181 includes thelocation wire 177 which connects the interface system 28 to the locatorelectrode 68 at the catheter's distal end 24. In this instance thetherapy supply line 161 is a chemical filled lumen 183. This lumenextends to the distal end 24 of the chemical delivery catheter 181 wherea needle 185 is used to infuse the chemical into the heart chamber wall125. During introduction of the chemical delivery catheter 181 into theheart chamber the needle 185 is withdrawn into the catheter body throughwithdrawal action 187. Once the location of the distal end 24 isdetermined to be at the site of interest the chemical delivery needle165 can be deployed through the reverse of withdrawal action 187.Potential chemicals to be used in the therapeutic delivery processinclude formaldehyde and alcohol.

Each of the therapy catheters 18 shown in FIG. 17 through FIG. 19 aswell as the radio frequency catheter shown in FIG. 2 can be miniaturizedand inserted into the coronary arterial tree. The location signalgenerated at locator electrode 68 can still be sensed by the passiveelectrodes 48 even though the signal is coming from the epicardium ofthe heart 16 rather than from within the heart chamber. Thus the movableelectrode location process of FIG. 15 can be used in this instance tohelp determine the location of the distal end 24 of the therapy catheter18 in the coronary arterial tree and whether it is close to a site ofabnormal electrical activity. Assuming that a site of ischemia willcommonly be a site of abnormal electrical activity, the MELP will alsoenable more rapid location of potential sites for angioplasty.

FIG. 20 shows an embodiment of the therapy catheter 18 using ballooninflation to supply the therapy. This angioplasty catheter 191 includesthe location wire 177 which connects the interface system 28 to thelocator electrode 68 at the catheter's distal end 24. In this instancethe therapy supply line 161 is an inflation media supply lumen 193 andthe therapy deployment apparatus 60 is an angioplasty balloon 195. Inuse, a site of interest would be determined after viewing the wallelectrogram generated by the WEGP of FIG. 10. Next the angioplastytherapy catheter 191 would be positioned in the coronary arterial treeand its position determined relative to the site of interest. Next, whenthe distal end 24 of the angioplasty catheter 191 was at the properlocation the balloon 195 would be deployed to open the artery. Finally,the electrical activity of the site would be reviewed to determinewhether the underlying tissue 125 was now receiving a proper bloodsupply and thus was no longer electrically abnormal.

1. A process for measuring electrophysiologic data in a heart chambercomprising the steps of: positioning a set of passive electrodes withinpatient's heart; positioning a set of active electrodes within apatient's heart; supplying oscillating current to said set of activeelectrodes thereby generating an electric field in said heart chamber;detecting said electric field at said passive electrode sites,generating a set of field measurement data; extracting in the timedomain, from said field measurement data, that component of said fieldmeasurement data corresponding to the underlying electrophysiologicactivity of the heart chamber, and generating electrophysiology data;graphically displaying said chamber geometry data; and graphicallydisplaying said electrophysiologic data.
 2. A process for determiningand displaying the location of a therapy catheter in a heart chambercomprising the steps of: positioning a set of passive electrodes withinsaid heart chamber; positioning a set of active locator electrodeswithin said heart chamber, said locator electrodes being positioned on atherapy catheter; supplying oscillating current to said set of activelocator electrodes thereby generating an electric field in said heartchamber; detecting said electric field at said passive electrode sites,and generating field measurement data; extracting in the frequencydomain, from said field measurement data, that component of said fieldmeasurement data corresponding to locator electrode location andgenerating location data; and graphically displaying said location data.